1. Field of the Invention
The present invention relates to a semiconductor device and, more specifically, relates to a semiconductor device including a switching element.
2. Description of the Related Art
High electron mobility transistors (HEMTs) including gallium nitride (GaN) compound semiconductors have been conventionally known. HEMTs have low on resistance and high breakdown voltage and are used in power applications, for example.
Kaneko (U.S. Pat. No. 7,859,021 B2) discloses a HEMT having a normally-off characteristic. This HEMT has a characteristic of going into an off state in the absence of a control signal applied to the gate electrode. In the off state, no current flows between the source and drain electrodes. Accordingly, it is not necessary to generate a negative control signal (negative potential) used to control the gate electrode, thus simplifying the structure of an electric circuit for driving the HEMT.
The HEMT disclosed in Kaneko, which has a normally-off characteristic, includes: a main semiconductor region having a two-dimensional carrier gas layer; a source electrode and a drain electrode which are located on a main surface of the main semiconductor region and are electrically connected to the two-dimensional carrier gas layer; a gate electrode located between the source and drain electrodes on the main surface of the main semiconductor region; and a metal-oxide semiconductor film located between the main surface of the main semiconductor region and the gate electrode. The metal-oxide semiconductor film is composed of materials such as a nickel oxide. This HEMT does not have an insulated gate structure but has a structure in which the gate electrode is laid on the main surface of the main semiconductor region with the metal oxide semiconductor film interposed therebetween. Moreover, it is known that HEMTs not having an insulated gate structure use materials capable of forming a Schottky contact with the main semiconductor region, such as nickel, for the gate electrode.